Prior to the present invention as shown by A. J. Chalk et al., Journal of Polymer Science, Part A-1, Vol. 7 (1965) pp. 2537-2545, silicone-polyarylene ether copolymers were made by anionic graft polymerization of lithiated poly(2,6-dimethyl-1,4-phenylene ether) with hexamethylcyclotrisiloxanes. In addition, Krantz, U.S. Pat. No. 3,668,273, assigned to the same assignee as the present invention and incorporated therein by reference, shows the synthesis of silicone-polyarylene ether block copolymers by effecting reaction between a hydroxy-terminated polyphenylene ether and an amino-terminated polydiorganosiloxane. The resulting organopolysiloxane-polyphenylene ether block copolymer is comprised of chemically combined polyphenylene ether blocks joined to polydiorganosiloxane blocks by silicon-oxygen-phenyl bonds.
Organopolysiloxanes have also been copolymerized with polyarylene polyether copolymers as shown by Strachen et al., U.S. Pat. No. 3,539,655, and Noshay et al., U.S. Pat. No. 3,539,656. The aforementioned siloxane-polyarylene polyether copolymers are reported as being hydrolytically stable as distinguished from copolymers having aryloxy-silicon linkages.
The present invention is based on our discovery that trimellitic anhydride acid chloride-modified polyphenylene ethers, referred to hereinafter as "PPE-TAAC", as shown by Aycock et al., U.S. Pat. No. 4,642,358, assigned to the same assignee as the present invention and incorporated herein by reference can be directly reacted with an amine-terminated polydiorganosiloxane to produce a polyphenylene ether-polydiorganosiloxane block copolymer having improved impact strength as compared to the starting polyphenylene ether referred to hereinafter as "PPE". In addition, unlike the silicone-polyether block copolymers of the prior art, the silicone-polyether copolymers of the present invention comprise polyphenylene ether blocks joined to silicone blocks by silicon imide linkages. It also has been found that substantially similar results can be obtained by effecting reaction between polyphenylene ether which has been modified with maleic anhydride referred to hereinafter as PPE-MA by coextruding a mixture of polyphenylene ether and maleic anhydride as described hereinafter.